Newish motherboards all turn off automatically if they don't get information from CPUFAN (most of the time CPUFAN1) make sure you always plug your heatsink into this power slot on the motherboard instead of SYSFAN or AUXFAN or any other power connection. Sometimes CPUFAN isn't the closest one to the socket.
Symptoms of this are basically the computer turns on for 1-3 seconds and either beeps extremely fast or (most often) just turns back off.

Thats my favorite (and only) tip since It sticks in my mind after build 2 was up but not staying on

Newish motherboards all turn off automatically if they don't get information from CPUFAN (most of the time CPUFAN1) make sure you always plug your heatsink into this power slot on the motherboard instead of SYSFAN or AUXFAN or any other power connection. Sometimes CPUFAN isn't the closest one to the socket.Symptoms of this are basically the computer turns on for 1-3 seconds and either beeps extremely fast or (most often) just turns back off.

yes I know - I gave Peanya a name check as I've used most of what he did for new builds and also included the follow up to his post. It was also his great post that got me started on this. I've had some time on my hands lately and thought it would be useful just to bring everybodies efforts here up to date, in one place and to include support for problems with existing systems.

So I've added a non new build section, Power Supply section and general troubleshooting tips; mostly from these boards but also from other places and my own experience.

In the end I'm hoping to make a comprehensive and readable guide to get people passed the first steps of troubleshooting before posting. I'm also happy to keep it up to date and expand it as necessary. I'm already conscious that it's predominantly hardware related and sections on common software problem and maybe a virus/spyware starter would be useful.

Hie there, i've read the post, just want to post my problem don't have
time to test now:

I have a new motherboard AsRock VIAPT880 P4, the the PC won't turn
on, it's like there's no power from the cable, but the cable is connected
properly, here's the thing, i tried to unplug the ATX 2.03 connector
and connect it again, i did not unplug the cable from the PC and when
the connector touched receiver, like half of the way not the click the we
expect to hear to be properly connected, the PC turned on and the CPU
FAN star to work normaly, but I got scared because the ATX connector
was not properly connected so i not brutally but quickly finished the "way"
and connected to hear the click then... the PC just shuts down.
Tried to turned it on using the button and nothing.
What the hell... my Power Supply is a 230w (max 300, at least is what is
written there) my old motherboard was micro-atx.
Could this be the problem?

this post should really be in the tech help section; not many people will see it here - maybe a mod will shift it for you if he sees it..........

It seems you could have a poor connection into the motherboard power socket. If you look at the male PSU connector, from the top, you'll see the individual brass pins inside each of the small plastic sockets. Make sure that none of them are pushed out - they should all be pushed right in.

With all the power leads disconnected push the connector into the board 5 or 6 times to clean the connectors. Then push it on totally.

Clear the CMOS and see if it retarts.

That PSU may well be underpowered but you'd need to tell us what the specifications of it are - usually printed on the case - and the rest of your PC set-up before we could be sure